Tropical data assimilation: theoretical aspects

Abstract In this chapter, some of the theoretical issues underlying the application of optimized methods of data assimilation to the tropical oceans are discussed. By “optimized” methods of data assimilation, we mean methods which minimize some objective measure of error. Methods formulated in this way are cast in terms of statistical hypotheses, which can be tested by standard statistical methods. The efficacy of simple models of the tropical ocean has been a major advantage in the practice of data assimilation for this region. We discuss physical reasons for the effectiveness of these simple models, but also remind the reader that much of this apparent simplicity stems from the nature of the agenda in tropical oceanography. Since the focus in the community is on phenomena relevant to ocean-atmosphere interaction and climate prediction, the highest priority is large scale, low frequency low latitude motions. More complex models are necessary for reasonably accurate descriptions of the dynamics of the tropical ocean on shorter spatial or temporal scales, or more than about 10° from the equator. We discuss some of the theory of the data assimilation methods as such, and conclude that the crucial research issues revolve around the prior error estimates that largely determine the product of any practical data assimilation method.

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